igneous
Granitic Pegmatite
Granitic Pegmatite (principally Quartz, Potassium Feldspar, and Mica)
Hardness: 6-7 (Mohs scale); Color: Pinkish-tan (feldspar), smoky gray/white (quartz), black (mica); Luster: Vitreous to pearly; Crystal structure: Very large, interlocking crystals (phaneritic/pegmatitic texture); Cleavage: Perfect in feldspar and micas.
- Hardness
- 6-7 (Mohs scale)
- Luster
- Vitreous to pearly
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Physical properties
Hardness: 6-7 (Mohs scale); Color: Pinkish-tan (feldspar), smoky gray/white (quartz), black (mica); Luster: Vitreous to pearly; Crystal structure: Very large, interlocking crystals (phaneritic/pegmatitic texture); Cleavage: Perfect in feldspar and micas.
Formation & geological history
Formed from the final, water-rich stages of a cooling magma chamber deep within the Earth's crust. The high water content allows for rapid ion diffusion, creating exceptionally large crystals.
Uses & applications
Source of rare earth elements, gems (like tourmaline or beryl), feldspar for ceramics, and quartz for glass. High-quality samples are used as geological specimens.
Geological facts
Pegmatites are famous for containing the largest crystals ever found on Earth, with some individual crystals reaching several meters in length. They are essentially 'giant-grained' granite.
Field identification & locations
Identify in the field by the unusually large size of the individual mineral grains (usually >1cm). Commonly found in the cores of mountain ranges or within metamorphic shields.
